The invention applies to a blood lancet device for withdrawing blood for diagnostic purposes. It comprises a housing with an outlet opening for the lancet tip, a lancet holder for holding the lancet and movable along a predetermined, straight puncturing path within the housing, and a lancet guide, guiding the lancet holder along the predetermined puncturing path.
In order to obtain a drop of blood, the blood lancet device must be pressed with a contact surface located around the outlet opening, against the skin (in particular against the finger tip or the earlobe). Subsequently, a pricking process is performed. During the pricking process, the lancet holder and the lancet held by it are moved along the predetermined puncturing path with high speed, driven by a lancet drive located in the blood lancet device, until the lancet tip comes out of the outlet opening and generates the wound necessary for obtaining the blood drop. After that, the lancet holder is driven back, by the lancet drive, into a position with the lancet tip inside the housing.
Lancet devices of this type are already known in many designs. In most cases, the lancet drive is a simple mechanism driving the lancet holder directly by a linear spring, being stopped by a thrust block at the point of the longest protrusion of the lancet tip. This stops the lancet abruptly; the spring action returns the lancet into its initial position. Such a blood lancet device can be produced simply. It is, however, not optimal with respect to its function, in particular as the pain caused by the prick is relatively high.
However, reduction of the pain caused by wound generation is of high medical importance. This is particularly true for diabetics, who must control their glucose level frequently and regularly, in order to adapt the necessary insulin injections to their requirements (depending on factors as e.g. food ingestion, physical activity and others), thus, if possible, always keeping the glucose level within defined target limits. This is of highest importance for the health of those patients, especially for the avoidance of serious late injuries, as e.g. amaurosis. Comprehensive investigations have shown that a tight glucose level control can dramatically reduce serious late injuries caused by diabetes mellitus.
Blood lancet devices which convert the relaxation movement of the drive spring by means of a rotatable drive rotor into the prick movement allow blood withdrawal with little pain. The vibration caused by the impact of the lancet holder onto a thrust block can be avoided.
U.S. Pat. No. 4,924,879 describes a blood lancet device with a rotor drive of that type, driving the rotor by a coaxial coil spring. The rotation movement of the rotor is converted to the linear movement of the lancet by means of a push rod system.
In the lancet device described in U.S. Pat. No. 5,318,584, the drive rotor has a rotation axis parallel to the prick direction. Here, it is also driven by a coaxial coil spring. The conversion of the rotational movement into the necessary linear movement of the lancet holder is performed by a rotary drive, preferably realized by a cam control. In this mechanism, a pivot of the lancet holder meshes with a corresponding recess in the rotor. This design allows a very good pricking behavior with low vibrations and a precisely reproducible pricking depth. This makes the pain, occurring with the wound generation, very small. However, a disadvantage of this system is the necessity of components with relatively complex shape which have to interact in a very precise way. Thus, their production is expensive. A precise manufacturing is the condition for a reliable function.
Based on this, the invention addresses the problem to provide a blood lancet device which achieves a pricking behavior which is low in vibrations and precise, and which can be produced with less manufacturing expense, thus reducing production costs.
With a blood lancet device of the type described above, with a rotor driven lancet holder, this task is obtained in the following way: The drive rotor has a pressure surface which is directed radially outwardly and runs with varying center distance around the rotation axis in such a manner that it has a vertex with maximum center distance, and a propelling section following the vertex against the sense of rotation, with a center distance decreasing against the sense of rotation. The drive spring is adapted for effecting in a propelling angle section of the rotation of the drive rotor via a pressure element a pressure with a component in radial direction to the rotation axis onto the propelling section of the pressure surface, thus driving the drive rotor by the pressure of the drive spring onto the pressure surface in the propelling section in the sense of rotation. The drive rotor is coupled via an output-side coupling mechanism with the lancet holder, in such a manner that the tip of the lancet protrudes from the outlet opening at a point of time in which the drive rotor is in the propelling angle section.
The drive rotor having a pressure surface which is directed in radially outward direction (away from the rotation axis) can be easily produced as a plastic part. The power transmission from the drive spring to the rotation movement of the drive rotor (subsequently called xe2x80x9cdrive-side coupling mechanism of the lancet drivexe2x80x9d) is determined by the form of the drive section of the pressure surface. Thus, different required drive rotor movement characteristics (rotation speed depending on rotation angle) can be adjusted by different designs of the pressure surface. A form with a propelling section which is, at least in parts of the propelling section, convex, has proven advantageous.
For tensioning, the drive rotor must be moved into a position where the pressure element is in contact with the pressure surface at the vertex. This can be obtained with different tensioning mechanisms. Preferably, not only the prick movement drive, but also the tensioning of the lancet drive is realized by an interaction of the spring and the pressure surface. To this end the pressure surface has a tensioning section with a center distance from the rotor center which increases against the sense of rotation. The tensioning section, too, has a convex shape, at least in a partial section thereof.
According to another preferred design, the output-side coupling mechanism, which converts the rotation movement of the drive rotor to the pricking and retraction movement of the lancet holder, is formed by a recess rotatable with the drive rotor, forming an operating cam and meshing with a pivot connected to the lancet holder. This design allows a variation of the output-side coupling mechanism, according to the desired pricking behavior, a corresponding variation of the form of the operating cam. This results in comprehensive possibilities for optimization of the speed profile of the pricking movement (dependence of current speed from lancet holder position) with respect to a pain which is as low as possible. A particularly simple design is obtained if the recess forming the operating cam is located in the drive rotor.